The present invention relates to an improvement of a screw-type jack and, more particularly, to a screw-type which is provided with an auxiliary screw barrel to be screw-fitted with a supporting table in a known telescopic triple-stage jack, to thereby widen a range of the extended jack length when it lifts.
Conventionally, a jack used as a screw-type jack mainly for an automobile is mostly a so-called telescopic triple-stage jack in which both stage numbers of inner extension/contraction type jack means and outer expansion/contraction barrel means are three in total.
Also, of another type of jack which is provided with an auxiliary screw barrel is known. Because the auxiliary screw barrel is of a male screw type in shape and is positioned at the center of the jack (on the inner side of a ram), the jack is of a telescopic double-stage type.
However, the conventional telescopic triple-stage jack has a defect in that a lift of the jack suffers a restriction of extension due to its structure reason in relation to the same type jack having a jack presents a problem is that the jack is liable to be broken because of insufficiency of the lift, or damaged when used under an unfavorable condition owing to an excessiveness of the lift.
To eliminate this problem, there exists a jack (telescopic quadruple-stage jack) in which lengths of the lifts at the respective stages are substantially the same. This type of jack includes a number of complicated parts and is inferior in performance so that it cannot operate appropriately.
Further, the conventional jack has been set in suit at a jack-up point by rotating a smaller bevel gear, but the operation of the gear requires much labor and it is difficult to rotate the smaller bevel gear due to a gear ratio between the smaller and larger bevel gears.